The ability to assemble nano-objects in rationally designed 3D superlattices can open tremendous opportunities for the fabrication of new classes of materials. However, such lattices are often difficult to predict and control and are dependent on a large number of factors. (Macfarlane R. J. et al. Science 334, 204-208, 2011, incorporated herein by reference in its entirety). For instance, for ionic solids, Pauling developed rules that explain the relative stabilities of different lattices of simple salts, but these rules do not allow for structure control because parameters such as size and charge of atoms (and small molecules) are not tunable (L. Pauling, The Nature of the Chemical Bond, Cornell Univ. Press, Ithaca, N.Y., ed. 3, 1960). In fact, changing an atom's size or charge inherently changes the electronic properties that affect relative lattice stability.
In contrast, nanoparticle-based superlattice materials should allow for more control over the types of crystal lattice that they adopt, given that one can tune multiple variables, such as nanoparticle size or the presence of different organic molecule layers on the nanoparticle surface, to control superlattice stability (C. A. Mirkin, et al. Nature 382, 607, 1996, incorporated herein by reference in its entirety). However, predictable architectural control still remains an elusive goal, regardless of the type of particle interconnect strategy chosen (see FIG. 1): electrostatic forces, covalent and noncovalent molecular interactions, and biologically driven assembly strategies (Nykypanchuk D, et al. Nature 451(7178), 549-52, 2008, incorporated herein by reference in its entirety).
A conceptually simple idea for overcoming this problem is the use of “encodable” interactions between building blocks. This can in theory be directly implemented using strategies based on DNA programmability to control the placement of nanoparticles in one and two dimensions as shown in FIG. 2. For example, U.S. Pat. Pub. No. 2009/0275465 to Gang et al. (incorporated herein by reference in its entirety) discloses the formation of three-dimensional crystalline assemblies of gold nanoparticles mediated by interactions between complementary DNA molecules attached to the nanoparticles' surface. The structure has the body-centered-cubic lattice structure, which is structurally open, with particles occupying only approximately 4% of the unit cell volume. Building on this development, U.S. Pat. Pub. No. 2009/0258355 to Maye et al. (incorporated herein by reference in its entirety) discloses a method of making three-dimensional crystalline assemblies or nanoclusters using anchoring biomolecules. These systems, however, entropically favor random geometry of connections during structure formation (see FIG. 3). Thus, it becomes difficult, if not impossible, to direct a desired lattice formation.
Recently much attention was focused on theoretical studies of patchy particles (Zhang et al. Langmuir 21(25) 11547-11551, 2005; incorporated herein by reference in its entirety) and shape directed assembly (Macfarlane, R. J. et al. Chemphyschem 11(15), 3215-3217, 2010; incorporated herein by reference in its entirety). These studies focused on the number and location of sites on spherical particles, which provide attractive interactions that determine many phenomena related to the complex structure formation in liquids, solids and gels (Starr, F. W. et al. Journal of Physics-Condensed Matter, 2006. 18(26): p. L347-L353; incorporated herein by reference in its entirety). Interestingly, the simple early models of colloidal patchy particles were found to correlate well with findings for atomic and molecular systems. For example, in a seminal work by Kolafa and Nezdeda, a water structure was captured by a model with tetrahedral connections. (Kolafa, J. and I. Nezbeda, Molecular Physics, 1987. 61(1): p. 161-175; incorporated herein by reference in its entirety). Formation of networks in silica was also explained using this approach by assuming low coordination and strong bond associations. Moreover, even the dynamics were successfully modeled, including the diffusion process, and interplay between a packing driven arrest, glass transition, bond-driven arrest, and gelation. A demonstrated high degree of similarity between basic models, described by coarse modeling and experimental observation in complex molecular systems, is indicative for an important role that directionality and geometry of connection plays in structure determination.
Therefore, it would be desirable to provide a solution, which overcomes the above-described inadequacies and shortcomings in the design and synthesis of the controlled crystal nanoparticle superlattices.